Typical of the drain valve prior art is U.S. Pat. No. 3,879,013 which discloses a drain boss which is capped off with a drain plug holding a poppet type valve open. When the drain plug is removed, the poppet closes to minimize fuel spillage. A separate hose or fitting is then threaded into the boss (where the plug was removed) which unseats the poppet and allows drainage. With the plug removed the valve becomes a standard push to drain type valve.
U.S. Pat. No. 3,026,897 discloses a standard type push to drain valve which can be pushed without removing a plug as in the above-mentioned patent. It also incorporates a hold open feature by threading the poppet to the cap and a feature whereby the primary seat may be replaced.
U.S. Pat. No. 3,703,189 also discloses a standard type push to drain valve. It features a design whereby the primary seat is removed by the poppet being lowered through the opening but not being completely removed.
None of the above prior art patents include any provisions for preventing accidental or inadvertant valve opening as for example by a blast force such as would be caused by lightning strikes. So far as is known the prior art is devoid of any better teaching in this regard.
Also in the general area of technology of the present invention and which may be of interest are the following U.S. patents:
U.S. Pat. No. 3,103,341 issued to Moran on Sept. 10, 1963 PA0 U.S. Pat. No. 882,170 issued to Schmidt on Mar. 17, 1908 PA0 U.S. Pat. No. 3,601,147 issued to Myers on Aug. 24, 1971.
Moran discloses a mechanically operated valve mounted externally on the tank and when opened by a screw device allows fluid to enter a chamber then into the hollow center portion of a rod. The rod is designed to allow a drain line to be attached to discharge the fluid.
Schmidt discloses a carburetor which incorporates a valve with two seats and flow passages through the valve to allow an air/gas mixture to pass to the upper seat area. When the valve is activated by the throttle, the air/gas mixture passes to the engine past both seats thereby suppling more mixture to the engine.
Myers discloses a semi-balanced valve with two seats similar to Schmidt. Passages are provided through the valve plug to allow static fluid pressure to pass through the valve plug to an upper chamber. The lower end of the valve plug is configured to create a negative pressure at the lower end of the plug as the valve is being opened which draws fluid from the upper chamber thereby reducing the pressure inside the valve plug and upper chamber.